Tiny Spyplanes May Recharge On Power Lines

A small unmanned aerial vehicle (UAV) able to recharge on power lines is under development by Defense Research Associates (DRA) and the Air Force Research Laboratory (AFRL). The PLUS (Power Line Urban Sentry) program UAVs will operate in confined urban spaces.

One of the major disadvantages of UAVs is that their small size limits their power supply, and therefore their usefulness. Patrick Marshall, a senior electronics engineer at AFRL, began investigating methods of charging small UAVs by flying them close to power lines. But the process was inefficient. "The best we could get was micro-watts of power," he said.

So Marshall built a toroidal test box that clamped around a power line to draw energy from the cable. The design was successful, though the latch mechanism needed work.

Phase II of the project involves the development of a power-line navigation ability. If GPS is jammed or unavailable, the power grid itself could guide the UAV.

The first prototype tests are expected in 2008.

In his excellent 1980 science/fantasy novel Changeling, Roger Zelazny describes small, autonomous surveillance craft called 'tracer-birds' that were also able to recharge far from home to continue operations:

The dark birdforms dotted the mountaintops like statues of prehistoric beasts, wings outspread. Had there been an eye to observe them, it might not even have noted their minute, tropism-like pursuit of the sun across the sky as they recharged their batteries for the night's flight.
(Read more about Roger Zelazny's tracer-birds)

Other methods of recharging UAVs are under development: take a look at Autonomous Soaring Project UAV Cloud Swift. Hawks and eagles glide on currents of rising warm air called thermals to extend their flight time without needing more fuel. Why not UAVs?